This invention relates generally to inkjet printers and more particularly to paper guides therefor.
A well known problem in inkjet printers is so-called "paper curl." Paper curl occurs due to the absorption of the liquid ink by the print media. This problem is especially prevalent in low humidity environments in which the print media is especially dry. Paper curl is somewhat of a misnomer, however, because transparencies as well as paper suffer from the paper curl problem.
The paper curl problem is illustrated in FIG. 1. In FIG. 1, a sheet of paper 10 is shown being fed out of an inkjet printer on a printer platen 12. The paper feed mechanism and printing mechanism are not shown for simplicity. As can be seen from FIG. 1, lateral edges 14 and 16 of the sheet 10 are bowed upwards away from the platen. The severity of the paper curl is determined by, among other things, the print time and the amount of ink deposited on the print media. The longer the print time and the more ink deposited, the more curl that occurs. Therefore, paper curl is especially pronounced in color printers which require multiple inks to be deposited to form a composite images. If the paper curl becomes too severe, the leading edge of the paper, shown coming out of the page in FIG. 1, can catch on a portion of the structure defining the paper path and become "jammed" inside the printer.
Referring now to FIG. 2, prior art paper guides 18 and 20 have been used to constrain the paper curl to an acceptable level. The paper guides 18 and 20 are mounted on the platen on opposite sides thereof to constrain a respective lateral edge of sheet 10.
Paper guide 20 is shown in more detail in FIG. 3. It can be seen in FIG. 3 that the lateral edge 16 of sheet 10 rides along the underside of paper guide 20. Because the paper contacts the paper guide, if there is printing on the sheet 10 in the area that contacts the paper guide, the printing will be smeared by the paper guide if the ink is not yet dry. To avoid this possibility, printers have constrained themselves from printing in the area on the paper that contacts the paper guide, i.e. the so-called "smear area." Thus, valuable printing space is given up in order to solve the paper curl problem. The amount of area given up can be significant if the paper guides are properly designed to account for paper misalignment and variation in paper widths. Accordingly, a need remains for a paper guide that can operate in worst-case operating conditions and yet has a larger maximum printable area.